1. Field of the Invention
The present invention relates to a gas-insulated switchgear for use in transformation of an electric power system and, more particularly, to an electric-field relaxation shield disposed in a disconnector part, a grounding switch part, or a conductor connecting part.
2. Description of the Related Art
FIG. 9 is a schematic view showing a structure of a conventional gas-insulated switchgear, and FIG. 10 is a sectional view thereof. In the drawings, a disconnector part 2 is accommodated in a grounding potential metal housing 1 filled with insulating arc-suppressing gas, and a moving side electrode part 2a and a stationary side electrode part 2b are respectively fixed and supported by spacers 3a and 3b made of an insulating material. The moving side electrode part 2a and the stationary side electrode part 2b are respectively provided with metal shields 4a and 4b in order to relax an electric-field value in the vicinity of the electrodes. A moving contact 5 coaxial with the disconnector part 2 passes through the centers of the shields 4a and 4b. This moving contact 5 is electrically connected to the moving side electrode part 2a and the stationary side electrode part 2b by moving contactors 6a and 6b respectively.
A grounding switch part 7 is located below the lower part of the disconnector part 2, and the moving side electrode part 2a of the foregoing disconnector part 2 and a stationary side electrode part 7b of the grounding switch part 7 are integrally formed in one body. In the same manner as the disconnector part 2, a moving side electrode part 7a and the stationary side electrode part 7b of the grounding switch part 7 are respectively provided with electric-field relaxation metal shields 8a and 8b. A moving contact 9 coaxial with the grounding switch part 7 passes through the center of the metal shields 8a and 8b. 
FIG. 11 is an enlarged view of a conductor connecting part 11 for connection between a main circuit conductor 10 and the spacer 3b of insulating martial shown in FIG. 10. The main circuit conductor 10 is in contact with a moving contactor 12, and the foregoing conductor connecting part 11 is covered with a metal shield 13, thus relaxing the electric-field value.
FIG. 12 is a schematic view showing another structure of a gas-insulated disconnector part disclosed in, for example, the Japanese Patent Publication (unexamined) No. 1990-46113 (FIG. 1 and upper right column of page 2). In this drawing, the moving side electrode part 2a and the stationary side electrode part 2b of the disconnector part 2 are respectively fixed and supported by posts 22a and 22b made of an insulating material. Insulating shields 23a and 23b are formed at ends of the moving side electrode part 2a and the stationary side electrode part 2b in the inter-electrode direction, thus relaxing the electric field between the electrodes. The moving contact 5 coaxial with the moving side 2a and the stationary side 2b of the disconnector part 2 passes through the center of the insulating shields 23a and 23b. This moving contact 5 is electrically connected with the moving side electrode part 2a and the stationary side electrode part 2b by the moving contactors 6a and 6b respectively.
In the above-mentioned conventional gas-insulated switchgear, it is necessary to arrange the metal shields 4a, 4b, 8a, 8b, and 13 each to have a large curvature in order to keep a low electric-field value in the vicinity of the electrodes. Hence a problem exists in that the disconnector part 2, the grounding switch part 7, and the conductor connecting part 11 are obliged to be large-sized, and it is therefore difficult to downsize the gas-insulated switchgear as a whole.
In the conventional gas-insulated switchgear, another problem exists in that it is necessary to secure a certain distance between the electrodes in order to keep a low electric-field value between the electrodes, and it is therefore difficult to downsize the gas-insulated switchgear also in axial direction.
In the case where any insulating material are used as the shield as shown in FIG. 11, the electric field is kept high on the surface of the insulating material, and a further problem exists in that the material deteriorates or breaks.
A still further problem exists in that an arc is generated at the time of opening and closing the contacts, which also results in deterioration.
In the case where the insulating materials are used simply as the shields without changing configuration of the metal parts, the electric field on the surface of the insulating material becomes higher rather than obtaining an advantage of reducing the electric field. Therefore, it is necessary to increase the distance between the electrodes or increase the insulating material in thickness after all, and the advantage of downsizing the entire equipment is hardly achieved.
The present invention was made to solve the above-discussed problems and has an object of providing a downsized gas-insulated switchgear and improving economical efficiency as a result of downsizing the gas-insulated switchgear.
To accomplish the foregoing object, a gas-insulated switchgear according to the invention includes: a grounding metal housing filled with insulating gas, and in which a disconnector part, a grounding switch part and a conductor connecting part are accommodated; and composite insulating shields integrally formed into one metal-dielectric shield in which surface of a high electric field part located in the vicinity of ends of openings is coated with a dielectric in such a manner as to cover electrode parts of the disconnector part, the grounding switch part and the conductor connecting part with the dielectric. In the mentioned composite insulating shield of at least one of the disconnector part, the grounding switch part and the conductor connecting part, a metal shield of less than 0.6 in non-uniform constant before coating the shield with the dielectric, is coated with a dielectric having a thickness of not more than approximately 30% of an inter-electrode distance from a facing electric-field relaxation shield or a charging part.
As a result, it is possible to effectively reduce the electric-field value in the vicinity of the electrodes at the disconnector part, the grounding switch part and the conductor connecting part, and it is possible to downsize the gas-insulated switchgear as a whole and improve economical efficiency as a result of downsizing the gas-insulated switchgear.